1. Field of the Invention
The present invention relates to methods for the manufacture of objects with small complex cross-sections, particularly optical fibres, micro-optical components, such as couplers, and micromechanical components.
2. Description of the Related Art
Fibre optics and integrated optic components are used in optical information technology and measuring techniques. Such components employ optical waveguides which determine their properties either as a result of their overall structure or by virtue of the cross-section of the waveguide or of external conditions.
Optical components in which the overall structure determines properties include star junctions and directional couplers in which two or more waveguides gradually converge or separate or are in close proximity over a defined length to such an extent that their fields interact. (See Unger, Optische Nachrichtentecknik, Bd.II Huthig-Verlag 1984.)
Components in which the cross-section of the waveguide determines its properties include integrated-optic acousto-optical beam deflectors in which light conducted by an elongated rectangular section of waveguide interacts with an acoustic wave propagating along the surface of the waveguide. (See F. Auracher, Planar Electro-optic and Acousto-optic Bragg Deflectors in: Integrated Optics, Hrsg. S. Martinelli, A. N. Chester, NATO ASI Series, Plenum Publication Corp., NY 1981.)
A known problem which arises with different components of the above types in optical measuring and information systems is the difficulty in coupling optical waveguides together in a low loss configuration. In most cases this problem can be overcome by using glass fibres which are highly flexible and can be adapted to most dimensional conditions. However such optical fibres usually have circular cross-sections and in the case of direct butt joints to different cross-sections and sizes of waveguide in various components high coupling losses occur (see A. Mahapatra et al. "Thermal Tapering of Ion Exchanged Channel Guides in Glass", Optical Letters, Volume 13, No. 2, 1988). Suitable coupling components must not only match in cross-section, shape and size but must also allow optical fields to match; that is although a change in optical modes may be allowed or required in passing through the coupling components, significant loss of optical energy must be prevented. Modes which radiate from the coupling components must not be generated.
Known solutions in the form of glass fibre bundles exist for these coupling problems when joining multimode waveguides having different cross-sections (see H. Naumann, G. Schroder, Bauelemente der Optik, Hanser-Verlag) or stacked optical waveguides--see U.S. Pat. No. 4,530,565 (David A. Markle). All these solutions are based on couplers formed by subordinate waveguides having cross-sections which are brought together at the ends of the coupler to conform with the different cross-sections of the waveguides which are to be coupled. The above mentioned U.S. Pat. No. 4,530,565 describes such an arrangement for joining square waveguides to elongated cross-sections or large radius arcuate cross-sections.
However no process has been disclosed for manufacturing coupling elements according to the above principles where waveguides have cross-sections small enough to allow mono-mode operation in at least one dimension. Such elements are used, typically, in integrated optic components for measurement and information technology.
As described in U.S. Pat. No. 3,989,495 and U.K. Patent Application 2,189,480, optical components having complex cross-sectional shapes can be drawn by plastic deformation from preforms including additional glass which is etched away after drawing.
In the field of endoscopes for medical and technical diagnostic uses, where bundles of optical fibres fixed to each other at each end but unattached throughout the rest of their length are used, methods of manufacturing are known in which individual fibres are surrounded with a soluble glass before bundling and the resulting preform is then drawn to give the required cross-section (see such U.S. Pat. Nos. 4,389,089, 3,669,772 and 3,830,667).